He also points out bottles of 1920s German wine that are still 'drinking beautifully'. "It's in imperial pints, " he says, "it's four glasses, which is basically a good lunchtime size."

They must have some amazing lunchtimes here.

Though we're surrounded by bottles, it wasn't until the mid 19th century that an act of parliament allowed merchants to sell wine in glass containers. Up until then, bottles had been hand-blown, and although they were roughly the capacity of the human lung, size was impossible to regulate. Wine, then was sold by the barrel, which explains some of the sloped flagstone floors down here, designed for barrel rolling.

Not all the vintages, alas, have kept. A crate or two of vintage Bollinger has been ruined, because it's been kept standing up (we all know bubbly should be kept on its side, right oenophiles?). Geordie won't get rid of them, because he likes the labels.

Air conditioning whirring above, he explains how keeping wine at a constant temperature is more important than the precise temperature itself. He recalls a time when he was working in Hong Kong and a CEO came to complain that the wine he'd bought from Berry Bros was 'completely cooked'. "I asked him if he was keeping the wine at a consistent temperature, and he said 'of course — I keep it in my office, which is always air conditioned.'

"He came back a few days later looking sheepish. He'd found out that the air conditioning switched off at three o'clock every morning."

If you're wondering if any of these antediluvian wines are for purchase, the short answer is no — although many are being kept for customers. (In a far bigger Berry Bros warehouse in Basingstoke, they're storing almost five million bottles for their customers.)

It's also a great Berry Bros tradition to crack open vintage wines with special guests over dinner upstairs — somewhere we'll get to a little later on.

But for a moment, let's step outside.

If you know the West End at all, chances are you'll have come across the black and gold frontage of Berry Bros & Rudd, on St James's Street. It's at home nestled among the cigar shops and gentlemen's clubs.

Bizarre, you might think, that the sign swinging above the door is that of a coffee mill.

In fact, when Berry Bros was opened in the very same establishment in 1698, it was a grocers that supplied coffee to the fashionable coffee houses of the time.

That explains the scales at the front of the shop — again, these are original. It became something of a tradition for celebrity customers of the day to be weighed on them — including Lord Byron, who was apparently self-conscious about his size, and Beau Brummell, who insisted on going through with it naked, to be sure of consistent results.

Such weigh-ins still happen now, and are still kept in ledgers like this one, which also record what the weigh-ee was wearing at the time (yeah, yeah, that top hat you're wearing definitely added on half a stone).

This part of the shop is what most Londoners will be familiar with — whether as a curious passer-by, or one of those savvy enough to know you can buy a bottle here, and consume it with a Cohiba at the cigar shop a few doors down.

No dearth of bottles — but almost all of them are empty. You're quite right in wondering where all the wine that's actually for sale is.

These days it's to be found in the new shop, opened in 2017. Its address may be Pall Mall, rather than St James's Street, but this is all part of the same complex — Berry Bros is a burgeoning beast (did we mention its offices in Hong Kong?).

Geordie Berry in the new Berry Bros shop. "If you know lots about wine, the supermarket can be a very good place to buy wine. If you know nothing about wine, it's better to go to a traditional merchant — they'll give you all the advice you possibly need."

A lot of people assume everything is very expensive, Geordie explains. The truth is, Berry Bros sell wines for as little as £8 or £9 a bottle.

And the priciest?

"£10,000."

You can buy tasters in the new shop

Although Berry Bros didn't want to create a 'Disneyland' version of the original shop, there is the odd nod to the past — such as these 100-year-old barrels lining the ceiling. "Does it still make you feel like you're in a whale's belly?" Geordie asks one of the shop assistants.

It's not all about the wine though, and this stained glass window in the new shop is a clue to that:

It's the logo for Cutty Sark whisky — the idea for this light blended whisky was conceived at Berry Bros. The ship was seen as a symbol of travel and adventure, and the whisky itself was shipped into prohibition-era America via the Bahamas and the Florida Keys by a man named Captain William McCoy. He could be trusted, says Geordie, because he was teetotal.

Berry Bros is also behind that gin which has a key 'embedded' into the bottle: the No. 3 London Dry Gin was invented for martini cocktails.

And ever been offered a nip of The King's Ginger at Christmas? That's a Berry Bros concoction too.

"We invented it for Edward VI back in 1903," explains Geordie, "He was one of the first people who had a car in London. He had an old Daimler — he used to whiz from estate to estate — and he was terribly worried he was going to catch his death of cold, so we were asked to create what was basically a driving liqueur."

How very un-PC.

Gems like the stained glass windows are merely scraping the surface. As we dive deeper into the depths beneath the floorboards we, we find these charming miniature wine bottles:

During the 1920s, Queen Mary commissioned an epic doll's house, which had electricity, running water, the lot.

Geordie's great grandfather was tasked honoured to make 1,200 miniature wine bottles, all with accurate labels, and — quite amazingly — all filled with a thimbleful of the corresponding vintage.

People didn't do things by halves back then.

And how about this toilet — decorated with copies of menus from Berry Bros dinners gone by. Dishes include turtle soup, boiled trout with white sauce — and the finest dessert of all: cigarettes.

We delve further and further in, one wine tasting room after the next. While some rooms go back centuries, Berry Bros is expanding down and outwards.

"Sometimes we knock down walls and find stuff," says Geordie.

The cellars alone now cover the size of two football pitches. Berry Bros hosts in the region of 300 wine schools a year.

Some of the architecture is relatively new, such as this, built in 2015

The curiosities keep on coming — Geordie shows us how wine tastings are often held on these wake tables — once used to support coffins in people's drawing rooms.

Speaking of drawing rooms, this is the one in which guests enjoy a glass of wine or champagne before one of those famous lunches or dinners.

And here's the room where many of those diners are held — four or five a week. It's decked out in genuine William Morris wallpaper, the fireplace in De Morgan tiles.

We ask Geordie if he ever finds it frustrating, or even sad, that he may taste the best wine he's ever had at one of these parties, and then never taste it again.

"You have those wonderful moments where you know you're never going to have it again. But the joy is that there's so much else to try."

The rooms keep on coming — every now and again we bump into someone. For such a historic place, it's wonderful to see it so lively.

These bottles, by the way, overlook Pickering Place — often cited as the spot where Britain's last sword duel was fought.

In fact, this is heavily disputed — not least because of its limited parameters for sword-wielding exploits. Still, Berry Bros was once very much in the wild west of the West End — Geordie shows us an antique map, which pictures the shop fringed by fields.

Rumours also abound of a secret tunnel linking Berry Bros to St James's Palace, at the bottom of the road. Is this another myth that should be scotched (so to speak)?

"It depends how you look at it," says Geordie. "What people have said is that there's every chance there might have been a tunnel at some point. But it doesn't appear on plans. The thing is we're always finding stuff, so whilst there absolutely isn't a door to a tunnel that is there at the moment — because Berry Bros was here almost before the rest of this part of London was here — there are lots of funny things.

"So the cellars go under the road, like they wouldn't in other parts of London — the road came after the building in a funny sort of way."